1. Field of the Invention
This invention relates to a hearing aid and, more particularly, to a hearing aid in which a reproducing transducer and a microphone are enclosed in one and the same housing.
2. Description of the Prior Art
In a conventional hearing aid wherein a reproducing transducer and a microphone are enclosed in one housing and are used at the same time, vibrations on the transducer side may be transmitted through the housing to the microphone side, thus resulting a resonance and deteriorated sound pickup sensitivity of the microphone. On the other hand, vibrations caused in the microphone due to its sound pickup operation may be transmitted through the housing to the reproducing transducer thus causing a resonance at the transducer and deteriorating its sound reproducing characteristics.
Moreover, when the transducer side vibrations are transmitted through the housing to the microphone side, the resulting resonance may be picked up by the microphone thus causing an acoustic feedback phenomenon known as howling.
Thus, in a certain prior art hearing aid, the transducer and the microphone are separated from each other by a partition wall mounted in the housing and are closely fitted in the housing by the medium of resilient rubber sheets for prohibiting transducer or microphone vibrations from being transmitted to the microphone or transducer through the housing and other connecting portions.
However, we have found that such separation of the transducer and the microphone by the partition wall and mounting them in the housing by the medium of rubber sheets or the like resilient means are not sufficient in general to prevent resonance from occurring between the transducer and the microphone and to prevent deterioration in their sound reproducing and sound pickup characteristics. Moreover, howling can not be prevented from occurring in such prior devices due to insufficient suppression of the resonance between the reproducing transducer and the microphone.
In another conventional hearing aid, the transducer and the microphone are mounted with a close fit between the housing wall and a support base plate by the medium of cushioning sheets made of rubber and similar resilient material and having plural peripheral projections, said base plate being provided in the housing and adapted for mounting of electrodes and other devices. Thus, vibrations produced at the transducer and microphone sides may be diffused or occasionally absorbed by these projections. However, since the vibrations per se may not be absorbed completely, such known device again is not sufficient to prevent the resonance between the transducer and the microphone and resulting howling, thus again giving rise to deterioration in the sound reproducing characteristics of the transducer and the sound pickup performance of the microphone.